The present invention relates to devices for supplying oil to valve actuating-system lash adjusters in overhead camshaft (OHC)-type engines.
In an OHC-valve actuating system a lash adjuster is commonly employed to automatically eliminate clearance between each valve stem and rocker arm. Typically, a lash adjuster is a hydraulic device, operated by oil pressure. Lash adjusters are illustrated and described in U.S. Pat. Nos. 4,009,696 to Cornell and 4,098,240 to Abell, Jr., the contents of which are incorporated herein by reference. To ensure proper and reliable operation, the oil pressure to each lash adjuster should be maintained low and constant under all conditions, so that lash adjuster pump-up, and, as a result, the opening of the valve will not hurt engine performance. Moreover, the amount of air bubbles in the oil supplied to each lash adjuster should be maintained as low as possible to prevent characteristic tapping sounds generated by the lash adjuster when air bubbles are conveyed to the high pressure chamber of the lash adjuster.
In conventional systems for supplying oil to lash adjusters, oil is pumped from an oil pan to a cylinder head through a main gallery of a cylinder block and is introduced into a camshaft housing. The oil is then returned to the cylinder head after it passes through an oil-delivery pipe provided on the camshaft housing, and is introduced into a long oil-supply passage for the lash adjuster, from which the oil is supplied to each lash adjuster.
In such systems, the oil pressure within the oil-supply hole for the lash adjuster rises with engine speed, thereby increasing the likelihood of lash adjuster pump-up problems. The conventional solution to this pump-up problem has involved the use of a special oil-pressure control valve or oil escape device, etc. to reduce the oil pressure supplied to the lash adjusters.
Also, fine air bubbles in the oil from the oil pump have caused problems since oil containing the air bubbles enters the high pressure oil chamber of the lash adjuster, as a result of which the lash adjusters lose their function as a fulcrum for the rocker arm. The conventional solution for this problem has been to provide a special air bubble-separating device or mechanism for the oil supplied to the lash adjusters.